In 2013, venture capitalist Aileen Lee coined the term "unicorn business" to describe a privately owned startup that had reached a $1 billion valuation. A business so rare that she named it after the mythical creature that has captured imaginations for centuries.

At the time, Lee had found only 39 of them. (The business kind, not the mythical creature).

Today they are a little less rare: there are over 1,500 around the world.

A few years ago, I decided to define a unicorn business a little differently (with apologies to any readers who are running billion-dollar startups).